Conventional optical emission spectrometers may include inductively coupled plasma (ICP) light sources for spectrochemical analysis. Generally, selecting light emitted along an axis of an ICP light source (axial viewing) for detection and measurement provides increased signal-to-background ratios, and consequently improved limits of detection, as compared to selecting light emitted along a direction perpendicular to the axis of the ICP light source (radial viewing). This advantage is particularly important for certain elements, such as arsenic (As), selenium (Se), lead (Pb) and others having optical emission lines in the ultraviolet region of the spectrum. However, under certain circumstances, selecting the light emitted perpendicular to the axis of the inductively coupled plasma source is advantageous, in that it enables measurement of a greater range of concentrations and allows optimization of the position of light selection to minimize inter-element interference effects. This may be particularly important for easily-ionized elements, such as potassium (K), sodium (Na), lithium (Li) and others having optical emission lines in the visible region of the spectrum. In addition, axial viewing generally provides high sensitivity and poor linearity, while radial viewing generally provides lower sensitivity and better linearity.
Attempts have been made to enable selection of light emitted along or perpendicular to the axis of an inductively coupled plasma source. For example, light for detection and measurement may be selected as required from either light emitted along the axis or light at right angles to the axis of the light source, but not both at the same time. That is, only one mode of viewing may be selected at any time. Accordingly, when a modern simultaneous spectrometer is used, for example, it is necessary to take separate measurements (e.g., separated in time) in each of the axial and radial viewing modes to obtain best performance for each element of interest. In order to achieve simultaneous axial viewing and radial viewing of the light, one spectrometer must be used for axial viewing and another spectrometer must be used for radial viewing. In other words, conventional systems require either two separate views using one spectrometer (increasing analysis time and sample consumption), or two simultaneous views, using separate spectrometers for each view (a very costly alternative).